Electrodynamic vibrator



18, 11944. H BENIOFF 2,346,655

ELECTRODYNAMIC VIBRATOR I I Filed April 18, 1941 5 Sheets-Sheet 1 1INVENITOR BY HUGO BENIOFF plillws, 19. H BENIOFF 2,345,655

ELECTRODYNAMIC VIBRATOR I Filed April 18, 1941 3 Sheets-Sheet 2 INVENTORHUGO ESENIQFF ATTORNEY April 18, 1944- H. BENIQFF ELECTRODYNAMICVIBRATOR 3 Sheets-Sheet 3 Filed April 18, 1941 Patented Apr. 18, 1944 I2,346,655 ELnc'rRonYNAMro vmnATon Hugo Benio', La Canada, Calif.,assigner to Sub marine Signal Company, Boston, Mass., a corporation ofMaine Application Api-u 1s, 1941, serial No. 389,209

(ci. 11i-sse) Claims.

The present invention relates to the art of sound transmission andreception by the use of compressional waves and more particularlyrelates to this art as applied to propagating media heavier than air,and in particular to the art of submarine signaling in frequency rangesin and' above the limit of audibility of the human ear for theproduction of .directive sound ywaves and the reception of sound wavesby directive receivers.

In the present invention for the reception of directive waves and Athepropagation of sound beams a plurality of similar vibrators mounted on aradiating element and operative in substantially the same manner yfroman electric source may be usedffor the creation of the sound'v waves.Each. vibrator in the present invention is lset into vibration by means'of the reaction between an alternating current flowing in a coilfastened to the vibrator and a. 'constant magnetic ield. These drivingcoils are mounted each at one end of the vibrators and the group thusforms a system for properly converting the electric energy to acousticenergy as will be more fully explained below.

In the present invention the electrical driving means is positioned atthe very end of the vibrating system where the greatest amplitude ofmotion of the vibrator is obtained. The driving element comprises acoil` rigidly mounted at one end of the vibrator in such a manner as notto interfere with the propagation of the mechanical or acoustic wave inthe tube upon which the'coil is mounted.

Further merits and advantages of the present invention will be morereadily understood from the description given in the specification belowand taken in connection with the drawings showing an embodiment of theinvention in which Fig. 1 shows a central section through the device;Fig. 2 shows a section on the line 2-2 of Fig. 1; Fig. 3 shows a sectionon the line 3-3 of Fig. l; Fig. 4 shows enlarged portion of a section ofFig. 1 with a slight modification inthe construction of the magnetic'circuit; and Fig. 5'shows a section on the line 5-5 of Fig. 1.

In the drawings there is provided a casing I on the forward end of whichmay be mounted a diaphragm 2 which may be round or hexagonal asindicated in Fig. 3. The central section 3 of this diaphragm is made ofa plate preferably integrally f formedwith the flange edges 4 and joinedto it by means of the continuous web running all the `way around thecentral heavy plate` 3. "The web 5, as indicated in Fig. 2, is in ahexagonal form,

but other forms may be used, depending upon the construction of thedrivingk units 6, the purpose 4being tonest the units 6 together in sucha fashion as to cover substantially the whole central section 3 of thediaphragm. 1

The unit 6 comprises a heavy base element 1 of hexagonal or otherdesirable form for nesting the units together, which base element 'Inarrows and tapers upward with sloping sides 8 to a symmetricallylocated mechanically vibratable tube 9 which is preferably formedintegral with the base member 1. The unit 6 as a whole is mounted to theplate 3 preferably by means of al centrally located machine screw I0passing through the base 1 and threading into the plate.3, clampingthe-unit E direct to the plate. It is essential that this joint be rigidand tight and preferably the joining faces are cemented together bymeans of cement indicated at II. The tube 9, which may be slottedlongitudinally, should have a diameter' approximately one-half that ofthe base member 1. A solid rod or bar with some mass atits free end maybe used in place of the tube 9 but in general the tube is preferable.The tube diameter should preferably in all cases be less than one-halfwave length of the wave propagated in the material of the u nit and itmay be smaller than this. Essentially the unit 6 and the section of theplate 3 immediately below it, to which the unit is fastened, formlongitudinally of-the tube a one-half wave length system at the desiredfre- 'quency of vibration with the'node near the base element I and inthis manner the vibration at the free end of the tube 9 may be madelarge compared with the amplitude of vibration in the plate 3. The freeend of the tube 9- is provided with a. coil I2 which may beindependently formed on a non-conducting form such as glass, Lucite, orsome such material, and rigidly cemented at the end of the tube 9. Thecoil I2 is short in length, generally not longer than approximatelyone-half the tube diameter. This coil is immersed in airgap I3 which issupplied with magnetic ux by means of the magnetic circuit comprisingthe shell I4 which is composed of an upper plate-like member I5 withdownwardly extending arms I6 and I6' by which the magnetic field unit isfastened to a soit iron plate member I1 by -means of the screws I8. lTheplate member I1 has its pole faces vI9 narrowed to increase the uxconcentra#- tion. The plate member I1 and.its pole pieces I9 arepreferably made of soft iron so as to offer a low reluctance path forthe magnetic ux, while the member lvwith its downwardly extending armsI6 ,and I6? maybe made of Alnico or some similar metal that provides avery powerful pervided with numerous airgaps I3.

22 around the central. core 20 might be iilled by means .of a directcurrent magnetizing coil 23. In this case, of course, it is preferableto make the central core 20 and the plate |5701 the same material and inone-piece and this, of course, would preferably be soft magnetic iron.The direct current magnetizing system may be supported by the plate I'Iresting upon a shoulder 24 on the wal1 25 oi. the casing I.

In the operation ofthe system, which may be 'used either as atransmitter or a receiver of sound waves, alternating current of theldesired frequency is impressed upon the coil I2 and direct current inthe magnetizing field unless a permanent magnet is used. The units 6will vi brate substantially independently at the driving frequency withequal amplitudes, thus providing a uniform vibration of the whole plate3. The device described is resonant at a frequency in which a. node isproduced in the tubes 9 near the base 1. The units 8 are made similarand all are similarly mounted so that the nodes in each unit formapproximately a plane parallel to the plane of the plate 3. By makingthe surface dimension of the plate 3 many times lthe wave length in themedium, the plate will produce a directive beam as a transmitter, and asa receiver will respond to waves approaching only from a correspondingsector generally normal tothe plate surface. l

Having now described my invention, I claim:

1. A device for producing or receiving compressional waves comprising,in combination, a casing having a radiating plate, a plurality ofelectrodynamically driven resonant vibrator units each comprising `asolid metallic base element having a` large mass comparative to the restof the resonant unit, each such base element being rigidly mountedwithin said casing on said radiating plate, said units each having acomparatively thin tube 'extending from the base and having at its freeend a driving coil, said tube comprising theelastic element of thevibrator and said base element being substantially inelastic in thevoperation of the vibrator, the combined elements forming with theradiating plate a half wave length resonant vibrating system meansproviding a magnetic eld in which each of said coils is positionedwhereby said device may be lised for sound transmission and sound recepion. 2. A device for producing or receiving compressional wavescomprising, in combination, a casing having a radiating plate, aplurality of electrodynamically driven resonant vibrator units eachcomprising a solid metallic base element havinga large mass 4comparativeto the rest of y the resonant unit, each such base element being rigidlymounted withinl said casing'on said radlating plate, said baseelementsbeing nested together in approximately abutting positions, said baseelements having comparatively thin tubes extending upwards andintegrally formed therewith, each having at their free ends a drivingcoil, said tube comprising the elastic element of the vibrator and saidbase element being substantially inelastic in the operation of thevibrator,-

the combined elements forming with the radiating plate a half wavelength resonant vibrating system and means providing magnetic ilelds foreach of said driving coils. n

3. A device ior producing or receiving compressional waves comprising,in combination, a casing having a radiating plate joined'thereto in athin web extending entirely around the plate,

. a plurality of electromagnetically driven resonant vibrator units eachcomprising a solid metallic base element having a large mass comparativeto the rest of the resonant unit, such units being nested togethercovering the entire plate and rigidly held thereto, said vibrators eachhaving extending from the 'side opposite said plate a comparativelysmall but elongated thin driving tube, the end of said driving tubehaving currentconducting means and means immersing saidcurrent-conducting means in a magnetic neld the vibrators with the tubeand base elements, together with the plate, forming a resonant, halfwave length, vibrating system.

4. A device for producing or receiving compressional'waves comprising,in combination, a casing hav-ing a radiating plate joined thereto in athin/ web extending entirely around the plate, a plurality ofelectromagnetically driven resonant vibrator units each comprising a.solid metallic base element having a large mass comparative to the restof the resonant unit, such `units being nested together and covering theentire plate and rigidly held thereto, said vibrators each havingextending from the side opposite said plate a comparatively small butelongated thin driving tube, the end of said driving tube havingcurrent-conducting means and means immersing said currentconductingmeans in a magnetic iield, said current-conducting means being short inlength compared to the length' of said tube and the vibrators with thetube and base elements, together with the plate, forming` a resonant,half wave length, vibrating system.

5. A device for producing or receiving compressional waves comprising,in combination, a casing having a radiating diaphragm, a great number ofelectrodynamically driven vibrators rigidly mounted and nested closelytogether on said radiating plate within said casing, said vibratorscomprising a small tube member-and a large end mass member having a basesubstantially llarger thanl the cross-sectional tube area. a drivingcoil short in length compared to the length of the tube mounted at theend of the tube and meanssupplying an electromagnetic field in whichsaid driving coil is positioned the vibrators with the tube and baseelements, together with vibrating system.

.HUGO BENIOFF.

